The present invention relates to transition-metal complexes of the general formula I or II, in particular as emitter molecules in organic electronic devices, to a layer and an electronic device which comprise the compounds according to the invention, and to a process for the preparation of the compounds according to the invention.
Chelate complexes and organometallic compounds are used as functional materials in a number of applications of different types which can be ascribed to the electronics industry in the broadest sense. In the case of organic electroluminescent devices based on organic components (general description of the structure cf. U.S. Pat. Nos. 4,539,507 and 5,151,629) and individual components thereof, the organic light-emitting diodes (OLEDs), the market introduction has already taken place. In spite of the successes that have already been achieved, further improvements are still desirable here.
In recent years, organometallic complexes which exhibit phosphorescence instead of fluorescence have increasingly been under discussion (M. A. Baldo, S. Lamansky, P. E. Burrows, M. E. Thompson, S. R. Forrest, Appl. Phys. Lett., 1999, 75, 4-6). For theoretical spin-statistical reasons, an up to fourfold increase in energy and power efficiency is possible using organometallic compounds as phosphorescence emitters. The main conditions that should be mentioned here for practical use are, in particular, a long operating lifetime, high stability to temperature stresses and a low use and operating voltage in order to facilitate mobile applications.
Besides the individual specific weak points for each material, the class of known metal complexes has a general need for improvement, which is described briefly below:                Many of the known metal complexes have low thermal stability (cf.: R. G. Charles, J. Inorg. Nucl. Chem., 1963, 25, 45). On vacuum deposition, this inevitably always results in the liberation of organic pyrolysis products, which, in some cases even in small amounts, considerably shorten the operating lifetime of OLEDs.        The strong interaction of the complex units in the solid, in particular in the case of planar complexes of d8 metals, such as platinum(II), likewise causes aggregation of the complex units in the emitter layer if the degree of doping exceeds about 0.1%, which is the case in accordance with the current prior art. This aggregation results in the formation of so-called excimers or exciplexes on excitation (optical or electrical). These aggregates frequently have an unstructured, broad emission band, which makes the generation of pure primary colours (RGB) considerably more difficult or completely impossible. In general, the efficiency for this transition also drops.        In addition, it is evident from the above-said that the emission colour is highly dependent on the degree of doping, a parameter which can be controlled precisely only with considerable technical effort, in particular in large production plants.        
Known in OLED technology are metal complexes of the group 10 transition metals (Ni, Pd, Pt) in which the central metal is bonded via two aromatic N atoms and two C atoms (WO 2004/108857, WO 2005/042550, WO 2005/042444, US 2006/0134461 A1) or two imine-like N atoms in combination with two phenolic O atoms (WO 2004/108857) or via two aromatic N atoms and two basic N atoms (WO 2004/108857). The known compounds have, inter alia, electroluminescence in the blue, red and green region of the electromagnetic spectrum.
Nevertheless, there is still a demand for further compounds which do not have the above-mentioned disadvantages and preferably exhibit electroluminescence in the blue, red and green region of the electromagnetic spectrum and in particular can also be employed in the solid state as light-emitting layer.